Ruthenium metal feature fill for interconnects

ABSTRACT

A method is provided for at least partially filling a feature in a substrate. The method includes providing a substrate containing a feature, depositing a ruthenium (Ru) metal layer to at least partially fill the feature, and heat-treating the substrate to reflow the Ru metal layer in the feature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and claims priority to U.S. ProvisionalApplication No. 62/171,739, filed Jun. 5, 2015, the entire contents ofwhich are herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to methods for void-less filling offeatures such as vias and trenches with low resistivity ruthenium (Ru)metal for microelectronic devices.

BACKGROUND OF THE INVENTION

An integrated circuit contains various semiconductor devices and aplurality of conducting metal paths that provide electrical power to thesemiconductor devices and allow these semiconductor devices to share andexchange information. Within the integrated circuit, metal layers arestacked on top of one another using intermetal and interlayer dielectriclayers that insulate the metal layers from each other.

Normally, each metal layer must form an electrical contact to at leastone additional metal layer. Such electrical contact is achieved byetching a feature (i.e., a via) in the interlayer dielectric thatseparates the metal layers, and filling the resulting via with a metalto create an interconnect. Metal layers typically occupy etched pathwaysin the interlayer dielectric. A “via” normally refers to any featuresuch as a hole, line or other similar feature formed within a dielectriclayer that provides an electrical connection through the dielectriclayer to a conductive layer underlying the dielectric layer. Similarly,metal layers connecting two or more vias are normally referred to astrenches.

The use of copper (Cu) metal in multilayer metallization schemes formanufacturing integrated circuits creates problems due to high mobilityof Cu atoms in dielectrics, such as SiO₂, and Cu atoms may createelectrical defects in Si. Thus, Cu metal layers, Cu filled trenches, andCu filled vias are normally encapsulated with a barrier material toprevent Cu atoms from diffusing into the dielectrics and Si. Barrierlayers are normally deposited on trench and via sidewalls and bottomsprior to Cu seed deposition, and may include materials that arepreferably non-reactive and immiscible in Cu, provide good adhesion tothe dielectrics and can offer low electrical resistivity.

An increase in device performance is normally accompanied by a decreasein device area or an increase in device density. An increase in devicedensity requires a decrease in via dimensions used to forminterconnects, including a larger aspect ratio (i.e., depth to widthratio). As via dimensions decrease and aspect ratios increase, itbecomes increasingly more challenging to form diffusion barrier layerswith adequate thickness on the sidewalls of the vias, while alsoproviding enough volume for the metal layer in the via. In addition, asvia and trench dimensions decrease and the thicknesses of the layers inthe vias and trenches decrease, the material properties of the layersand the layer interfaces become increasingly more important. Inparticular, the processes forming those layers need to be carefullyintegrated into a manufacturable process sequence where good control ismaintained for all the steps of the process sequence.

The problems associated with the use of Cu metal in increasingly smallerfeatures in a substrate will require replacing the Cu metal with otherlow-resistivity metals.

SUMMARY OF THE INVENTION

A method is provided for void-less Ru metal feature fill forinterconnects in a microelectronic device.

According to an embodiment of the invention, method is provided for atleast partially filling a feature in a substrate by providing asubstrate containing a feature, depositing a ruthenium (Ru) metal layerto at least partially fill the feature, and heat-treating the substrateto reflow the Ru metal layer in the feature.

According another embodiment, a method is provided for filling a featurein a substrate by providing a substrate containing a feature, depositinga conformal ruthenium (Ru) metal layer that fills the feature, andheat-treating the substrate to reflow the conformal Ru metal layer inthe feature, where the conformal Ru metal layer has seam voids in thefeature and the heat-treating seals the seam voids and increases thegrain size of the conformal Ru metal layer in the feature.

According to yet another embodiment of the invention, a method isprovided for at least partially filling a feature in a substrate byproviding a substrate containing a feature formed in a dielectric layeron the substrate, forming a nucleation layer in the feature, depositinga conformal ruthenium (Ru) metal layer on the nucleation layer to atleast partially fill the feature, and heat-treating the substrate toreflow the conformal Ru metal layer in the feature, where theheat-treating reduces voids in the feature fill and increases the grainsizes of the conformal Ru metal layer in the feature.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 illustrates dimensions of narrow features in a substrate used forRu metal fill according to an embodiment of the invention;

FIGS. 2A and 2B show cross-sectional and top view scanning electronmicroscopy (SEM) images of the features in a substrate used for Ru metalfilm filling according to an embodiment of the invention;

FIG. 3A shows cross-sectional SEM images of Ru metal deposition innarrow features in a substrate according to an embodiment of theinvention;

FIG. 3B shows cross-sectional SEM images of Ru metal deposition innarrow features in a substrate according to an embodiment of theinvention;

FIGS. 4A and 4B show cross-sectional SEM images of as-deposited Ru metallayer in features in a substrate according to an embodiment of theinvention; and

FIGS. 5A and 5B show cross-sectional SEM images of a heat-treated Rumetal layer in features in a substrate according to an embodiment of theinvention.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

Methods for void-less filling of features with low resistivity Ru metalfor microelectronic devices are described in several embodiments.

According to one embodiment, a method is provided for at least partiallyfilling a feature in a substrate. The method includes providing asubstrate containing a feature, depositing a Ru metal layer to at leastpartially fill the feature, and heat-treating the substrate to reflowthe Ru metal layer in the feature. The at least partial filling takesadvantage of capillary action to pull heat-softened Ru metal down intovery narrow features and recrystallization of the Ru metal to formlarger Ru metal grains. The inventors have discovered that this uniqueand unexpected result of low temperature Ru metal recrystallization andreflow can be used to replace Cu metal fill with Ru metal fill. Thelarge grain size of the reflowed Ru metal has low electrical resistancethat is needed for replacing Cu metal fill in narrow features. It hasbeen shown that Ru metal, with its short effective electron mean freepath, is an excellent candidate to meet International Technology Roadmapfor Semiconductors (ITRS) resistance requirements as a Cu metalreplacement at about 10 nm (5 nm node) minimum feature sizes. Due tomany material and electric properties of Ru metal, it is less affectedby downward scaling of feature sizes than Cu metal.

The feature can, for example, include a trench or a via. The featurediameter can be less than 30 nm, less than 20 nm, less than 10 nm, orless than 5 nm. The feature diameter can be between 20 nm and 30 nm,between 10 nm and 20 nm, between 5nm and 10 nm, or between 3 nm and 5nm. A depth of the feature can, for example be greater 20 nm, greaterthan 50 nm, greater than 100 nm, or greater than 200 nm. The featurescan, for example, have an aspect ratio (AR, depth:width) between 2:1 and20:1, between 2:1 and 10:1, or between 2:1 and 5:1. In one example, thesubstrate (e.g., Si) includes a dielectric layer and the feature isformed in the dielectric layer.

FIG. 1 illustrates dimensions of narrow features in a substrate used forRu metal fill according to an embodiment of the invention. The narrowfeatures were prepared by etching features in a Si substrate andthereafter depositing (backfilling) an oxide layer (SiO₂) in the etchedfeatures to reduce the diameter of etched features. The etched featureshad diameters of 50 nm, 56 nm, 64 nm, and 80 nm. The backfilled featureshad diameters (widths) of about 11.5 nm, about 14 nm, about 17.4 nm, andabout 28.5 nm, near the mid-depths of the features.

FIGS. 2A and 2B show cross-sectional and top view SEM images of thefeatures in a substrate used for Ru metal film filling according to anembodiment of the invention. Preparation of the features in thesubstrate was described in FIG. 1. The features in FIG. 2A had adiameter of about 14 nm, a depth of about 120 nm, an aspect ratio ofabout 8.5, and a pitch of about 112 nm. The features in FIG. 2B had adiameter of about 11.5 nm, a depth of about 110 nm, an aspect ratio ofabout 9.5, and a pitch of 100 nm.

FIG. 3A shows cross-sectional SEM images of Ru metal deposition innarrow features in a substrate according to an embodiment of theinvention. Preparation of the features in the substrate was described inFIG. 1. The features had diameters of about 11.5 nm, about 17.4 nm, andabout 28.5 nm. Prior to Ru metal deposition, a 15 Å thick TaN nucleationlayer was deposited in the features using atomic layer deposition (ALD)with alternating exposures oftert-butylimido-tris-ethylmethylamido-tantalum (TBTEMT,Ta(NCMe₃)(NEtMe)₃) and ammonia (NH₃) at a substrate temperature of about350° C. A conformal Ru metal layer with a thickness of 70 Å wasdeposited on the TaN nucleation layer by chemical vapor deposition (CVD)using Ru₃(CO)₁₂ and CO carrier gas at a substrate temperature of about200° C. FIG. 3A shows that the features having diameters or 11.5 nm and14.5 nm were effectively filled with Ru metal, whereas the narrowfeatures having a diameters 28.5 nm were not completely filled and had avoid in the upper part of the narrow features.

FIG. 3B shows cross-sectional SEM images of Ru metal deposition innarrow features in a substrate according to an embodiment of theinvention. Conformal Ru metal deposition of 150 Å shows that all thefeatures were effectively filled with Ru metal.

FIGS. 4A and 4B show cross-sectional SEM images of as-deposited Ru metallayer in features in a substrate according to an embodiment of theinvention. The Ru metal layer was deposited by CVD using Ru₃(CO)₁₂ andCO carrier gas at a substrate temperature of about 200° C., and thefeatures also contained a TaN nucleation layer as described in referenceto FIG. 3A. The SEM magnifications in FIGS. 4A and 4B are 200,000 and350,000, respectively. The ˜28 nm wide features at mid-depth are notcompletely filled but have a void in the Ru metal that is about 9 nmwide near the top of the features.

FIGS. 5A and 5B shows cross-sectional SEM images of heat-treated Rumetal in features in a substrate according to an embodiment of theinvention. The SEM magnifications in FIGS. 4A and 4B are 200,000 and350,000, respectively. The as-deposited Ru metal layer was heat-treatedat a substrate temperature of 450° C. in the presence of a forming gasfor 5 min. FIGS. 5A and 5B show that the heat-treating reflowed the Rumetal in the features to effectively fill the narrow features with Rumetal having large grain sizes, and reduced or eliminated voids in theRu metal feature fill. The filling takes advantage of capillary actionto pull heat-softened Ru metal down into the very narrow features.Further, any Ru metal seam voids in the feature are sealed by theheat-treating.

The structures in FIGS. 5A and 5B may be further processed, for exampleby performing a planarization process (e.g., chemical mechanicalpolishing (CMP)) that removes excess Ru metal from above the features.

According to some embodiments, the nucleation layer may be deposited inthe features by ALD or CVD prior to the Ru metal fill. The nucleationcan, for example, include a nitride material. According to oneembodiment, the nucleation layer may be selected from the groupconsisting of Mo, MoN, Ta, TaN, W, WN, Ti, and TiN. A role of thenucleation layer is to provide a good nucleation surface and an adhesionsurface for Ru metal in the feature to ensure conformal deposition ofthe Ru metal layer with a short incubation time. Unlike when using a Cumetal fill, a good barrier layer is not required between the dielectricmaterial and the Ru metal in the features. Therefore, in the case of aRu metal fill, the nucleation layer can be very thin and may benon-continuous or incomplete with gaps that expose the dielectricmaterial in the features. This allows for increasing the amount of Rumetal in a feature fill compared to a Cu metal feature fill. In someexamples, a thickness of the nucleation layer can be 20 Å or less, 15 Åor less, 10 Å or less, or 5 Å or less.

According to some embodiment, the Ru metal layer may be deposited byALD, CVD, plating, or sputtering. In one example, the Ru metal layer maybe deposited by CVD using Ru₃(CO)₁₂ and CO carrier gas. However, otherRu metal precursors may be used to deposit the Ru metal layer. In someexamples, the Ru metal layer may include a Ru-containing alloy.

According to embodiments of the invention, the Ru metal layer may bedeposited at a first substrate temperature and the subsequentheat-treating of the as-deposited Ru metal layer may be carried out at asecond substrate temperature that is higher than the first substratetemperature. For example, the heat-treating may be performed at asubstrate temperature between 200° C. and 600° C., between 300° C. and400° C., between 500° C. and 600° C., between 400° C. and 450° C., orbetween 450° C. and 500° C. Further, the heat-treating may be performedat below atmospheric pressure in the presence of Ar gas, H₂ gas, or bothAr gas and H₂ gas. In one example, the heat-treating may be performed atbelow atmospheric pressure in the presence of forming gas. Forming gasis a mixture of H₂ and N₂. In another example, the heat-treating may beformed under high-vacuum conditions without flowing a gas into a processchamber used for the heat-treating.

According to one embodiment, the heat-treating may be performed in thepresence of a gaseous plasma. This allows for lowering the heat-treatingtemperature compared to when a gaseous plasma is not employed. Thisallows the use of heat-treating temperatures that are compatible withlow-k and ultra-low-k materials. According to some embodiments, thefeatures may be formed in a low-k material with 2.5≦k<3.9 or anultra-low-k material with k<2.5. In one example, the gaseous plasma caninclude Ar gas. The plasma conditions may be selected to includelow-energy Ar ions.

According to another embodiment, prior to depositing the Ru metal layer,the substrate may be exposed to a treatment gas that modifies thesurfaces in the features and increases the nucleation rate of Ru metallayer in the features. In one example, the treatment gas can include anitrogen plasma, a NH₃ plasma, a NH₃ anneal, or a combination thereof.The exposure to the treatment gas can nitride the surfaces in thefeatures. In one example, the treatment gas increases the hydrophilicityof surfaces in the features and thereby increases the nucleation rate ofthe Ru metal in the feature.

In one example, the opening of a feature may pinch off (close) and avoid may form inside the feature before the feature is completely filledwith a Ru metal layer. According to one embodiment, the void may beremoved by removing excess Ru metal from above the feature, for exampleby a planarization process, thereby removing the excess Ru metal thatcaused the pinch off. Thereafter, the heat-treating process may beperformed to reflow the Ru metal layer in the feature. According to oneembodiment, this may be followed by depositing additional Ru metal layeron reflowed Ru metal layer and repeating the heat-treating process toachieve void-free filling of the feature.

Methods for void-less filling of features such as vias and trenches withlow resistivity Ru metal for microelectronic devices have been disclosedin various embodiments. The foregoing description of the embodiments ofthe invention has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. This description and theclaims following include terms that are used for descriptive purposesonly and are not to be construed as limiting. Persons skilled in therelevant art can appreciate that many modifications and variations arepossible in light of the above teaching. Persons skilled in the art willrecognize various equivalent combinations and substitutions for variouscomponents shown in the Figures. It is therefore intended that the scopeof the invention be limited not by this detailed description, but ratherby the claims appended hereto.

What is claimed is:
 1. A method for at least partially filling a featurein a substrate, the method comprising: providing a substrate containinga feature; depositing a ruthenium (Ru) metal layer to at least partiallyfill the feature; and heat-treating the substrate to reflow the Ru metallayer in the feature.
 2. The method of claim 1, further comprising:prior to depositing the Ru metal layer, forming a nucleation layer inthe feature.
 3. The method of claim 2, wherein the nucleation layer isincomplete with gaps that expose the substrate in the recessed feature.4. The method of claim 2, wherein the nucleation layer is selected fromthe group consisting of Mo, MoN, Ta, TaN, W, WN, Ti, and TiN.
 5. Themethod of claim 1, further comprising prior to depositing the Ru metallayer, exposing the substrate to a treatment gas that increases thenucleation rate of the Ru metal layer in the feature.
 6. The method ofclaim 5, wherein the treatment gas includes nitrogen.
 7. The method ofclaim 1, wherein the Ru metal layer is deposited by atomic layerdeposition (ALD), chemical vapor deposition (CVD), plating, orsputtering.
 8. The method of claim 7, wherein the Ru metal layer isdeposited by CVD using Ru₃(CO)₁₂ and CO carrier gas.
 9. The method ofclaim 1, wherein the substrate includes a dielectric layer and thefeature is formed in the dielectric layer.
 10. The method of claim 1,wherein the heat-treating is performed in the presence Ar gas, H₂ gas,Ar gas and H₂ gas, or H₂ gas and N₂ gas.
 11. The method of claim 1,wherein the Ru metal layer is deposited at a first substrate temperatureand the heat-treating is performed at a second substrate temperaturethat is greater than the first substrate temperature.
 12. The method ofclaim 11, wherein the second substrate temperature is between 200° C.and 600° C.
 13. The method of claim 1, wherein depositing the Ru metallayer pinches off the feature opening before the feature is filled withthe Ru metal layer, thereby forming a void inside the feature, themethod further including, prior to the heat-treating, removing excess Rumetal that caused the pinch off from above the feature.
 14. The methodof claim 13, further comprising depositing additional Ru metal layer onthe heat-treated Ru metal layer in the feature; and heat-treating theadditional Ru metal layer to reflow the additional Ru metal layer in thefeature.
 15. A method for filling a feature in a substrate, the methodcomprising: providing a substrate containing a feature; depositing aconformal ruthenium (Ru) metal layer that fills the feature; andheat-treating the substrate to reflow the conformal Ru metal layer inthe feature, wherein the conformal Ru metal layer has seam voids in thefeature and the heat-treating seals the seam voids and increases thegrain size of the conformal Ru metal layer in the feature.
 16. Themethod of claim 15, wherein the substrate includes a dielectric layerand the feature is formed in the dielectric layer.
 17. The method ofclaim 15, wherein the conformal Ru metal layer is deposited at a firstsubstrate temperature and the heat-treating is performed at a secondsubstrate temperature between 200° C. and 600° C. that is greater thanthe first substrate temperature.
 18. A method for at least partiallyfilling a feature in a substrate, the method comprising: providing asubstrate containing a feature formed in a dielectric layer on thesubstrate; forming a nucleation layer in the feature; depositing aconformal ruthenium (Ru) metal layer on the nucleation layer to at leastpartially fill the feature; and heat-treating the substrate to reflowthe conformal Ru metal layer in the feature, wherein the heat-treatingreduces voids in the feature fill and increases the grain sizes of theconformal Ru metal layer in the feature.
 19. The method of claim 18,wherein the conformal Ru metal layer is deposited at a first substratetemperature and the heat-treating is performed at a second substratetemperature between 200° C. and 600° C. that is greater than the firstsubstrate temperature.
 20. The method of claim 18, wherein thenucleation layer is selected from the group consisting of Mo, MoN, Ta,TaN, W, WN, Ti, and TiN.